Modern aircraft are equipped with growing numbers of electrical components that require power even when the aircraft is parked and all switches are off. The problem, according to Concorde Battery (Booth 3019), is that these parasitic loads can drain the battery to the point where it may allow engine start but not contain enough reserve power for emergencies.

“These loads are generally low amperage—typically under 50 milliamperes—but since they are continuously present they can deplete the battery’s capacity if the aircraft is inactive for an extended time,” the company explained. Parasitic loads include devices such as clocks, radios, onboard computers, and relays.

Another problem with allowing parasitic loads to drain the battery is that each time the battery is drained, its plates get sulfated. This makes the battery harder to charge and may cause premature failure, Concorde Battery said.

To combat this problem, Concorde Battery offers its Parasitic Load Test Adapter (PLTA), which enables the measurement of an aircraft’s parasitic loads. The PLTA connects between the MS3509 quick-disconnect receptacle and the aircraft’s mating plug. It is fitted with test leads that a technician can connect to a digital multimeter so its ammeter can be used to evaluate the parasitic load.

If the load causes the battery to deplete 10 percent of its capacity in a certain period, and if the aircraft sits for longer than that period, then some mitigation will be required. That could include charging the battery between flights.

Another way to eliminate the parasitic load is simply to disconnect the battery when the aircraft isn’t flying, and this is relatively easy with a quick-disconnect plug. Concorde Battery recommends, however, consulting with the aircraft manufacturer to make sure this is a safe process that won’t harm any components in the aircraft. In some cases, modifications may be available to reduce the load.